1. Field of the Invention
The present invention relates generally to a vehicle which is equipped with a number of performance/safety enhancing arrangements such as four wheel steering, four wheel drive, active suspension and the like type of systems and more specifically to a control which integrates and optimizes the operation of the same.
2. Description of the Prior Art
JP-A-59-77968 discloses an example of a 4WS steering arrangement wherein, when the vehicle speed is low and the steering of the front wheels is large, reverse phase steering of the rear wheels is implemented to reduce the turning circle. On the other hand, when the vehicle speed is high and the steering angle of the front wheels is relatively small, inphase steering of the rear wheels is implemented for the sake of cornering stability.
JP-A-61-157437 discloses an example of a four wheel drive arrangement wherein when wheel slip occurs the distribution of drive power to the vehicle wheels is adjusted in a manner which improves stability during sudden applications of power, acceleration etc.
However, when the above mentioned 4WS and 4WD systems are both utilized in the same vehicle, the combined effect of the two systems is apt not to be optimal. The reason for this is that consideration has not been given to the overall system and the sensitivities of the auxiliary steering control of the 4WS and the driving force distribution control of the 4WD are set individually and arranged so that they operate independently of one another. Conditions which induce a large response in the auxiliary steering system are different from those which induce a similarly large response in the drive power distribution. Accordingly, when one system is put into effect the other tends to remain dormant and does not supplement the effect of the one which is currently effective. Even when both of the systems are simultaneously active, as the two systems are controlled independently of one another, still the effect of one tends to be small and the total effect promimates that which could be achieved by equipping the vehicle with only one of the two arrangements. Further, the provision of the two systems undesirably increases the total energy consumption with respect to the total effect which is achievable.
It has been thought to link the two systems in a manner which provides a cooperative control between the two systems with a view of improving a given facet of one control, or modifying one control to compensate for the degradation of the performance of the other system. Nevertheless, the effect is limited to given facets of operation and the overall on total performance of the two systems is not synergistically improved.